The present invention relates to security documents including a security image area composed of a printed security image and a printed complementary security image. The security image area is arranged to provide an indication of document authenticity.
Conventional security documents comprise a security image area including security image elements and complementary security image elements designed such that an attempted duplication or reproduction results in the formation of a readily apparent warning image on the face of the duplicate document. The security image elements and the complementary security image elements are arranged such that the presence of the security image and the security image elements is not readily apparent on the original. Examples of security documents of this type are illustrated in U.S. Pat. Nos. 4,579,370, 5,149,140, 5,197,765, 5,340,159, the disclosures of which are incorporated herein by reference.
The above-described conventional security documents can be said to provide a negative indication of validity because the alteration created by the attempted duplication results in the formation of a warning image on the face of the attempted duplicate. There is, however, no positive indication on the original document that it is valid. Rather, the security image is merely arranged to provide a warning message on the attempted duplicate. Accordingly, there is a need for a security document production wherein a positive indication of validity may be gleaned from the original document, regardless of whether an attempt has been made to duplicate the document.